Chlorine biocides are widely adapted and used due to its various applications and advantages. However, chlorine biocides have disadvantages which are widely recited both in the literature and in the patent art. Bromine biocides have numerous conventional applications and are considered the “gold standard” for cooling towers, due to its many advantages over chlorine. These benefits of bromine chemistry in comparison to chlorine include, but are not limited to: enhanced performance at alkaline pH values above 7.5; enhanced performance in the presence of ammonia and other nitrogenous materials; and enhanced performance against biofilms, i.e. bacteria residing on surfaces rather than in solution. Accordingly, bromine biocides are particularly useful in controlling biofouling.
Typically, bromine biocides perform their functions through hypobromous acid (HOBr), which in turn is usually formed by reacting chlorine bleach (either hypochlorous acid (HOCl) or hypochlorite (NaOCl)) with sodium bromide (NaBr). Chlorine bleach solution can be mixed with sodium bromide solution, although the two components must be kept separate until mixing or immediately before the bromine biocide application as it is known that combining the two solutions (chlorine and sodium bromide) are highly reactive. U.S. Pat. No. 5,464,636 discloses the separate feeding of solutions for generating a biocide for use in a cooling tower through the use of separate chlorine and bromine feeders. The conventional generation inherently possesses numerous health, safety and/or environmental concerns.
Solid compositions of both chlorine and sodium bromide are available and benefit an end user by only needing one product rather than two separate liquid solutions. Such solid products containing both chlorine and sodium bromide are known; however the dispensing disadvantage of stability and control over the safety of the reaction to generate the bromine biocide present challenges for use of this solid technology.
Stable solid disinfectant compositions, disclosed in U.S. Pat. No. 2,815,311 to the Diversey Corporation in 1957, is an early example of a solid bromine biocide composition. Further advances throughout the years have been focused on improving the stability of the chlorine and NaBr combination. Other patents that describe a tablet containing a combination of a chlorine species with a bromide ion source include U.S. Pat. Nos. 4,557,926 and 5,015,643.
U.S. Pat. No. 5,688,515 to Occidental Chemical Corporation in 1997 claims a method for increased stability for a combination of trichloroisoyanuric acid and sodium bromide. Using such product for a small recirculating water system, an operator usually adds one or more disinfectant tablets by hand into the water system, and the added tablets are submerged into a bulk of water. With enough water around the tablets, the reaction between trichloroisoyanuric acid and sodium bromide forms hypobromous acid (HOBr) as the three reactions shown below proceed to the desired product.

Using such product for larger cooling towers, putting the tablets or blocks into the bulk water becomes impractical and not desirable, thus an automated feeder or dispenser is preferred. However, there exists a need for improved dispensing and dosing of the biocide. In such a feeder, the tablets must be wetted and dissolved prior to introduction into the cooling water stream. It is in those feeders, the reaction between trichloroisoyanuric acid and sodium bromide generates both bromine gas and HOBr. This is distinct from adding such a tablet (or other solid) directly into bulk water, as in such direct addition to bulk water the large excess of water will drive the reaction to produce more HOBr. In such a reaction there is excess water to solubilize any newly formed bromine gas, which is distinct from the dispenser where less water is present and therefore less capability to solubilize the formed bromine gas.
Bromine gas is a noxious, pungent smelling, reddish-brown gas. The gas can lead to severe corrosion of equipment. In addition, the gas is a health hazard to personnel operating the blending and tableting units, and still further the produced gas could cause an explosion if generated in sufficient quantities under pressure.
U.S. Pat. No. 5,688,515 acknowledged drawback of the potential for significant gas release when a tablet is wetted and the consequences as the result of it. The reference teaches that moisture adversely affects the water stability of tablets or solid compositions of chlorine and sodium bromide. Moisture causes a reaction to occur between the trichloroisocyanuric acid and sodium bromide particles which results in the formation of bromine gas.
Other approaches have been used to prevent HBrO to escape once it has been formed. For example, U.S. Pat. No. 5,464,636 discloses the combination of either trichloro- or dichloro-isocyanuric acid together with sodium bromide. It is stated that once the chlorine and bromine species react in situ to form hypobromous acid (HOBr), that newly formed HOBr can evaporate from the recirculating water system. The authors seek to limit the evaporation of the HOBr from the use solution by the addition of a “bromine volatilization suppressant.” However, the disclosed method is to prevent evaporation from the use solution and does not address gas release from the solid product during the dispensing process.
Despite the various approaches taken to solve the problem associated with dispensing a solid composition to produce the bromine biocide HBrO, this problem remains unsolved. Thus, using a product that contains both chlorine bleach (either hypochlorous acid (HOCl), hypochlorite (NaOCl), or precursor thereof) and sodium bromide (NaBr) in water towers presents opportunities for enhanced safety and conditions for operation.
Accordingly, it is the objective of this invention to reduce the amount of bromine gas produced by using a chlorine bleach and bromide product in water towers.
It is a further objective of the claimed disclosure to provide a dispensing mechanism for reducing the amount of gas evolution when reacting sodium bromide with chlorine.
A further object of the disclosure is to produce stable and safe solid biocides for various applications of use.
Other objects, advantages and features of the present disclosure will become apparent from the following specification taken in conjunction with the accompanying drawings.